Spectrum sharing between primary users and co-existence groups of secondary users

ABSTRACT

Embodiments assign shared spectrum resources to access points. Embodiments group the access points into coexistence groups of access points, and generate a vertex graph including vertices that each represent one of the coexistence groups, where an edge connecting a pair of vertices in the vertex graph represents an overlap between coverage contours of a pair of coexistence groups represented by the pair of vertices, and the edge is assigned a weight that is proportional to the overlap as compared to other overlaps between coverage contours of other pairs of coexistence groups. Embodiments generate at least one vertex-colored graph by assigning a color to each vertex in the vertex graph, group the coexistence groups into groups of coexistence groups based on their corresponding assigned colors in the at least one vertex-colored graph, and map shared spectrum transmit frequencies to the groups of coexistence groups.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Nonprovisional applicationSer. No. 15/900,151 (filed Feb. 20, 2018), which claims the benefit ofProvisional Application 62/600,489 (filed Feb. 22, 2017), each of whichapplication is incorporated herein by reference in its entirety.

FIELD

The present disclosure generally relates to wireless communication, andmore specifically, to wireless spectrum sharing and interferencemanagement.

BACKGROUND

Wireless communication refers to communicating voice, data, or any otherinformation over a wireless medium such as air. Unlike wired mediumswhich are available only to transmitters/receivers that are physicallyconnected to the medium, a wireless medium is inherently open andshared. Therefore, certain frequency bands (also referred to as bands,frequencies, frequency channels, or channels) of a wireless medium maybe dedicated to certain users in order to guarantee communicationquality and bandwidth availability. The demand for wireless spectrum hasbeen continuously increasing with the increase in the number of wirelessusers (e.g., commercial cellular operators). One way to address thisdemand is to open the bands that have been previously dedicated tocertain users. An example is the 3550-3700 MHz band (the 3.5 GHz band)which was previously reserved for military use but has been opened bythe U.S. Federal Communications Commission (“FCC”) for shared use.Similarly, the 1695-1710 MHz, 175-51780 MHz, and 2155-2180 MHz bands(the “AWS-3” bands) have also been considered for shared use wheneverfederal incumbent systems relocate out of them.

When sharing spectrum, the users of the shared spectrum (e.g., federaland non-federal incumbent systems, access points of commercial cellularoperators, etc.) should not interfere with one another, and in case of ausage conflict, higher priority users should be guaranteed access to theshared spectrum. In the 3.5 GHz band, the FCC has defined a three-tieredmodel of users, where incumbent users (e.g., federal and non-federalincumbent systems) are positioned at the top tier and have the highestpriority, while public users (e.g., commercial cellular operators,emergency vehicles, police, etc.) are positioned at either a middle tieror a bottom tier. Specifically, some public users may obtain higherpriority under a Priority Access License (“PAL”) and be positioned inthe middle tier and have medium priority, while other public users mayoperate without a license under General Authorized Access (“GAA”) and bepositioned in the bottom tier and have the lowest priority. Each PAL andGAA public use device may implement a communication system that operatesaccording to a wireless communication technology or standard protocol(e.g., Long Term Evolution (“LTE”), Wideband Code Division MultipleAccess (“WCDMA”), Global System for Mobile Communications (“GSM”), etc.)to communicate with one or more end user devices (e.g., smartphones).

One or more Spectrum Access Systems (“SASs”) may facilitate spectrumsharing among the incumbent and public users. The SASs monitorinterference and dynamically assign frequency bands to various devicesthat consume shared spectrum resources such that devices with a lowerpriority do not interfere with those with a higher priority.

SUMMARY

Embodiments provide methods, systems, and computer-readable medium forassigning shared spectrum resources to access points that provide theresources to end users such as smartphone or other devices. Embodimentsgroup the access points into coexistence groups of access points, andgenerate a vertex graph including vertices that each represent one ofthe coexistence groups, where an edge connecting a pair of vertices inthe vertex graph represents an overlap between coverage contours of apair of coexistence groups represented by the pair of vertices, and theedge is assigned a weight that is proportional to the overlap ascompared to other overlaps between coverage contours of other pairs ofcoexistence groups. One embodiment generates at least one vertex-coloredgraph by assigning a color to each vertex in the vertex graph, groupsthe coexistence groups into groups of coexistence groups based on theircorresponding assigned colors in the at least one vertex-colored graph,and maps shared spectrum transmit frequencies to the groups ofcoexistence groups, where each access point in a group of coexistencegroups is configured to transmit using a transmit frequency that isassigned to the group of coexistence groups by the mapping. However,using colors for grouping coexistence groups as represented by verticesin a graph is only one possible abstraction method, and alternativeembodiments may group such vertices using other abstraction methods,e.g., by assigning labels, letters, etc.

One embodiment provides a computer-readable medium storing instructionsthat, when executed by a processor, cause the processor to assign sharedspectrum resources to access points. The assigning includes grouping theaccess points into coexistence groups of access points; generating avertex graph including vertices that each represent one of thecoexistence groups, where an edge connecting a pair of vertices in thevertex graph represents an overlap between coverage contours of a pairof coexistence groups represented by the pair of vertices, where theedge is assigned a weight that is proportional to the overlap ascompared to other overlaps between coverage contours of other pairs ofcoexistence groups; generating at least one vertex-colored graph byassigning a color to each vertex in the vertex graph; grouping thecoexistence groups into groups of coexistence groups based on theircorresponding assigned colors in the at least one vertex-colored graph;and mapping shared spectrum transmit frequencies to the groups ofcoexistence groups, where each access point in a group of coexistencegroups is configured to transmit using a transmit frequency that isassigned to the group of coexistence groups by the mapping.

One embodiment provides a network system including one or more serversand two or more Spectrum Access Systems (“SASs”) implemented as softwaremodules hosted on the one or more servers, where the two or more SASsare configured to communicate with each other and with access points toassign shared spectrum resources to the access points, the assigningincluding: grouping the access points into coexistence groups of accesspoints; generating a vertex graph including vertices that each representone of the coexistence groups, where an edge connecting a pair ofvertices in the vertex graph represents an overlap between coveragecontours of a pair of coexistence groups represented by the pair ofvertices, where the edge is assigned a weight that is proportional tothe overlap as compared to other overlaps between coverage contours ofother pairs of coexistence groups; generating at least onevertex-colored graph by assigning a color to each vertex in the vertexgraph; grouping the coexistence groups into groups of coexistence groupsbased on their corresponding assigned colors in the at least onevertex-colored graph; and mapping shared spectrum transmit frequenciesto the groups of coexistence groups, wherein each access point in agroup of coexistence groups is configured to transmit using a transmitfrequency that is assigned to the group of coexistence groups by themapping

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute part ofthis specification, and together with the description, illustrate andserve to explain various embodiments.

FIG. 1 illustrates a system for forming a vertex-colored graph ofcoexistence groups of access point, according to an embodiment of thedisclosed subject matter.

FIG. 2 illustrates a schematic diagram for assigning weights to edges ina vertex-colored graph of coexistence groups of access point, accordingto an embodiment of the disclosed subject matter.

FIG. 3 illustrates a schematic diagram for performing a cut on avertex-colored graph of coexistence groups of access point, according toan embodiment of the disclosed subject matter.

FIG. 4 illustrates a schematic diagram for assigning specificfrequencies to groupings of coexistence groups of access point,according to an embodiment of the disclosed subject matter.

FIG. 5 illustrates a schematic diagram for controlling power levels ofvarious access points to limit aggregate interference levels in anincumbent area of protection, according to an embodiment of thedisclosed subject matter.

FIGS. 6A-6D provide bar graphs related to the Effective IsotropicRadiated Power (“EIRP”) of various access points, according to anembodiment of the disclosed subject matter.

FIG. 7 is a flowchart for assigning shared spectrum resources to variousaccess points, according to an embodiment of the disclosed subjectmatter.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings.Wherever possible, the same reference numbers are used in the drawingsand the following description to refer to the same or similar parts.While several illustrative embodiments are described herein,modifications, adaptations, and other implementations are possible. Forexample, substitutions, additions, or modifications may be made to thecomponents illustrated in the drawings, and the illustrative methodsdescribed herein may be modified by substituting, reordering, removing,or adding steps to the disclosed methods. Accordingly, the followingdetailed description is not limited to the disclosed embodiments andexamples. Instead, the proper scope is defined by the appended claims.

Embodiments described herein allow for spectrum sharing betweenincumbent users and coexistence groups of secondary users. Embodimentsgenerate a vertex-colored graph including vertices that each represent acoexistence group of access points and use the vertex-colored graph togroup the coexistence groups so that access points in each group ofcoexistence groups can be assigned the same frequency of the sharedspectrum. One embodiment defines an objective function that accounts forobjectives such as access point bandwidth and coverage areas, costsrelated to interference and switching, and constraints such as minimumaccess point bandwidth and power. The embodiment uses the objectivefunction along with the vertex-colored graph to perform power andfrequency assignment over coexistence groups of access points.Accordingly, embodiments allow for more efficient spectrum sharing.

Coexistence Groups

In shared spectrum environments involving incumbent users (primaryusers) and secondary users, secondary user system resources such asbandwidth and power may be allocated by a Spectrum Access System (“SAS”)such that incumbent protection, secondary user fairness, spectrumefficiency (e.g., bps/Hz/km²), and Quality of Service (“QoS”, e.g.,interference, stability, etc.) are ensured. A SAS may be implemented assoftware modules hosted on servers which may be on one or more cloudplatforms. A cloud platform may include a distributed system having oneor more software processes executed over a local or distributed networkusing at least one computer server or other computer hardware, asdescribed below with reference to an example embodiment illustrated inFIG. 1. The hardware may include computing devices (e.g., desktops,workstations, etc.), handheld computing devices, memory devices, networkcomponents, and/or interface components, which allow for network-basedcomputing and shared resources over a distributed network. Cloudservices are trusted by many of the largest federal and commercialenterprises in part because of the robust controls available to maintainsecurity and data protection on a cloud platform. A cloud platform alsoprovides flexibility with respect to resource allocation and remoteaccess. The SAS receives information about components of a wirelessenvironment (e.g., base stations, wireless users, other SASs, requestsby incumbent users for exclusive use, etc.) and allocates sharedspectrum resources to various users/devices in the wireless environmentaccordingly.

In some embodiments, secondary users may operate as part of a“coexistence group”. A coexistence group is a network or set of accesspoints managed by a certain operator, where the access points in thecoexistence group desire a common frequency assignment from the SAS. Inone embodiment, the mutual interference and channel assignments of thecollection of Citizens Broadband radio Service Devices (“CBSDs”) and/ornetworks in a coexistence group are coordinated by the SAS using a setof coexistence policies. Each coexistence group is defined under theconstituency of a SAS, and coordination of coexistence groups definedunder different SASs is performed through SAS-to-SAS interface. In oneembodiment, coexistence group spectrum management policies are commonacross all SASs in order to address consistency and transparencyrequirements. To that end, the SASs share their views of theircoexistence groups to obtain a common view of the environment. Anexample of the policies/methods based on which coexistence groups aremapped to channels is graph coloring as disclosed herein with referenceto various embodiments.

In some embodiments, if multiple SASs are contending for a common sharedspectrum resource pool, the SASs need to coordinate with one anothersince one SAS's frequency assignments impact all others, andinterference aggregated across the SASs needs to be controlled to ensureincumbent protection.

In some embodiments, coexistence groups that do not interfere with oneanother may use the same frequency/frequencies, thus leading to improvedspectrum efficiency. In some embodiments, a coexistence group is notassigned frequencies that are the same as nearby incumbents. In someembodiments, resource assignments (e.g., transmit power assignments)across coexistence groups are made in some fair way, e.g., proportionalto the number of access points in a coexistence group.

Graph Coloring

In some embodiments, the SASs perform resource allocation across thecoexistence groups by generating a vertex-colored graph based on thecoverage contours of each of the coexistence groups. However, vertexcoloring is only one possible abstraction method, and alternativeembodiments may use other abstraction methods (such as assigning labelsor letters to the vertices) and use such alternative abstraction methodsin a same or similar manner as a vertex-colored graph described below. Avertex-colored graph is made of one or more vertices, where each vertexmay be connected by an edge to one or more other vertices, and eachvertex is assigned a color such that no edge is connecting two verticesthat have the same assigned color. In one embodiment, for example, thecoverage contour of a coexistence group may be the union ofSAS-determined individual downlink coverage areas of the access pointsin that coexistence group. The SAS may generate the vertex-colored graphsuch that each coexistence group is represented as a vertex in thevertex-colored graph, and two vertices of the graph are connected if thecoverage contours of their corresponding coexistence groups overlap. TheSAS may then assign a color to each vertex by using any known graphcoloring method apparent to a person skilled in the relevant arts. Inone embodiment, for example, the SAS may implement any known “minimumvertex coloring” method to color the vertices using the fewest number ofcolors such that no edge is connecting two vertices that have the sameassigned color.

FIG. 1 illustrates a system 1000 for forming a vertex-colored graph 1024by one or more SASs 1026 based on coverage contours 1002, 1004, 1006,1010, 1012, 1014, 1016, 1018 of eight coexistence groups that eachinclude one or more access points 1008. Each of the SASs 1026 may beimplemented as one or more software modules hosted on a cloud platform1032 and executed by a server 1028 in the cloud platform 1032. Althoughthe SASs 1026 in the embodiment of FIG. 1 are illustrated as beinghosted on and executed by the same server 1028, in alternativeembodiments, the SASs 1026 may be hosted on separate servers and/orexecuted by more than one server or by a network of distributed servers.The SASs 1026 communicate with respective access point 1008 to generatethe vertex-colored graph 1024 and store it on a memory 1030 in the cloudplatform 1032. The vertex-colored graph 1024 is made of vertices 1025and edges 1027, where each vertex represents one of the eightcoexistence groups, and each edge represents an overlap between coveragecontours of coexistence groups represented by the vertices that areconnected by that edge.

Due to the coverage contour overlap configuration in the example of FIG.1, the vertex-colored graph 1024 includes two separate connected sets ofvertices: a first connected set 1020 and a second connected set 1022. Aconnected set of vertices is a set of vertices in which each vertex isconnected to at least one other vertex in the connected set. The firstconnected set 1020 includes those vertices that represent coexistencegroups 6, 7, and 8, while the second connected set 1022 includes thosevertices that represent coexistence groups 1, 2, 3, 4, and 5.

The first connected set 1020 and the second connected set 1022 areseparate from each other since there is no coverage contour overlapbetween the coexistence groups represented by vertices in the firstconnected set 1020 and the coexistence groups represented by vertices inthe second connected set 1022. Accordingly, disconnected portions of thevertex-colored graph 1024 allow for partitioning of the coexistencegroups into those represented by the first connected set 1020 and thoserepresented by the second connected set 1022 such that each connectedset represents a set of coexistence groups that can be consideredindependently in shared spectrum resource assignment because thecollective coverage area represented by the first connected set 1020does not interfere with the collective coverage area represented by thesecond connected set 1022 and vice-versa. That is, the set ofcoexistence groups represented by each connected set can reuse theentirety of the available shared spectrum, assuming that incumbentprotection is guaranteed.

In some embodiments, a weight may be assigned to each edge in avertex-colored graph to indicate a relative amount of interferencebetween the pair of coexistence groups represented by the vertices thatare connected by that edge, as compared to the other edges. In oneembodiment, for example, the amount of interference indicated by aweight assigned to an edge may be proportional to the amount of overlapin the coverage areas of the two coexistence groups represented by thevertices that are connected by that edge. FIG. 2 illustrates a schematicdiagram 2000 for assigning weights 2002 to edges 2004 that connectvertices 2020 of a vertex-colored graph 2006 formed based on coveragecontours 2008, 2010, 2012, 2014, 2016 of five coexistence groups thateach include one or more access points 2018 (the colors assigned to eachvertex of the vertex-colored graph 2004 are not illustrated in FIG. 2).In the example of FIG. 2, since the coverage contours of coexistencegroups 1 and 2 have about three times the overlap area of the coveragecontours of any other pair of overlapping coexistence groups (e.g.,coexistence groups 3 and 5), the weight assigned to the edge thatconnects the vertices that represent coexistence groups 1 and 2 in thevertex-colored graph 2006 is “3” while the other edges are assigned aweight of “1”.

Resource Assignment Optimization

After generating a vertex-colored graph based on the coverage contoursof the coexistence groups of access points, the SASs may use thevertex-colored graph along with an objective function to determine anoptimum assignment of shared spectrum resources to a set of secondaryusers that request access to such resources. In some embodiments, forexample, the objective function may have as objectives the bandwidthassigned to each access point and the coverage area achieved by eachaccess point. The coverage area may be calculated based on the accesspoint downlink using any SAS-standardized propagation model known in therelevant arts. Alternatively or additionally, the objective function mayaccount for costs such as the interference between coexistence groups,for example, based on the weights assigned to the edges connectingvertices representing coexistence groups in the vertex-colored graph.Alternatively or additionally, if it is desirable to maintain networkstability (i.e., not require access points to change channels or powerassignments), the objective function may account for the cost of“switching” to capture the negative impact of a candidate assignmentrequiring some access points to switch channels or power assignments.Alternatively or additionally, the objective function may account forconstraints such as incumbent protection and any guard bands that may beneeded between frequency assignments to access points. Alternatively oradditionally, the objective function may account for fairnessconsiderations that may demand a certain minimum assignment of sharedspectrum resources to each coexistence group, such as a minimumbandwidth assignment and a minimum transmit power level for each accesspoint.

In one embodiment, for example, the objective function may be formed as:

f _(BW)(ΣBW_(i))+f _(CA)(ΣCA_(i))−Σf _(j)(C _(j))

where BW_(i) is the i^(th) access point bandwidth, f_(BW) is a functionof the sum of the access point bandwidths, CA_(i) is the i^(th) accesspoint coverage area, f_(CA) is a function of the sum of the access pointcoverage areas, and f_(j) is a function of the j^(th) cost C_(j). Thefunctions f_(BW), f_(CA), and f_(j) may be selected based on therelative importance of their corresponding objective (i.e., bandwidth orcoverage area) or cost. In one embodiment, for example, one or more ofthese functions may be a linear function of the correspondingobjective/cost. In alternative embodiments, one or more of thesefunctions may be a more complicated function such as a step function oran exponential function.

In one embodiment, for example, the criteria used for forming theobjective function may include objectives, costs, and constraints, wherethe objectives include assigned bandwidths BW_(i) and coverage areasCA_(i), the costs include the cost of interference C_(I) (e.g.,proportional to the coverage area overlap of coexistence groups) and thecost of CBSD channel switching Cs, and the constraints include minimumaccess point bandwidth and power assignments considering fairness,incumbent protection, and guard bands. However, the objective functionfor shared spectrum resource assignment optimization may be formed usingalternative and/or additional objectives, costs, and constraints aswould be apparent to one skilled in the relevant arts.

In some embodiments, in order to reduce disruptions, shared spectrumresource assignment optimization may be applied periodically (e.g., onceper day/week), and access point channel/power assignment changes aremade only if such changes provide significant improvement over thecurrent state. In these embodiments, some headroom may be allocated oneach SAS so that the SAS may temporarily assign frequency and transmitpower to CBSDs that request grants between the periodic updates. Ifthere are no new CBSDs requesting service during the interval betweenupdates, the headroom may be applied to existing CBSDs under somefairness considerations.

Coordinated Resource Assignment

In some embodiments, multiple SASs may generate a same/commonvertex-colored graph of coexistence groups of access points and applythe same objective function to obtain coordinated shared spectrumresource assignment over the access points. In these embodiments, theSASs may share information relevant to the coordinated shared spectrumresource assignments and agree on coordination policies to quantify theamount of interference between coexistence groups of access points, andtherefore operate as a collective SAS with information about all accesspoints and coexistence groups and agreed upon methods for coordinatedinterference management. In one embodiment, for example, the coordinatedinformation may include the interference weights between coexistencegroups of access points.

In one embodiment, the SASs coordinate on a policy (reconciliationprocess) to quantify the interference weights. For example, in oneembodiment, if there are two SASs managing access points within each oftwo coexistence groups, each SAS calculates an estimate of theinterference weight between the two coexistence groups, and the SASsthen use an agreed upon reconciliation process (e.g., coordinated weightis the average of each SAS's interference weight estimate) to determinethe interference weight used in coexistence calculations by both SASscollectively.

The coordinated information may allow each SAS to generate the samevertex-colored graph of coexistence groups of access points. In oneembodiment, if a single SAS manages all the access points in a connectedset, SAS-to-SAS coordination is not required to ensure incumbent/primaryuser protection, and therefore that single SAS may use any optimizationmethod it desires so long as the optimization method satisfies anyrequired fairness constraints.

Suboptimum Resource Assignment

In some embodiments, finding the shared spectrum resource assignmentsthat optimize the objective function is a Nondeterministic PolynomialTime (“NP”)-complete problem requiring an exhaustive search overcandidate solutions. If there are only a small number of access points,an exhaustive search for the best shared spectrum resource allocationgiven an NP-complete objective function may be practically implementedand thus desired. However, in many circumstances (e.g., when the numberof access points is large), an exhaustive search across all resourceassignment options is prohibitively complex, hence a suboptimum approachusing a reduced search space may be needed. In one embodiment, forexample, only a subset of the resource assignment options is considered.In some embodiments, the search space may be reduced to a small numberof candidate solutions to be investigated, and the reduced search spacetypically includes a solution that is optimum or close to optimum.

Grouping of Coexistence Groups

In some embodiments, the search space for finding a solution to optimizethe objective function may be reduced by grouping the coexistencegroups. The following embodiments describe some example groupingoptions. However, other variations or extensions to the followingembodiments to provide additional candidates for consideration would beapparent to those skilled in the relevant arts.

In one embodiment, in each connected set in the vertex-colored graph ofthe coexistence groups of access points, the represented coexistencegroups may be grouped according to their assigned colors in thevertex-colored graph such that the coexistence groups with the sameassigned color are grouped together. Since there is an edge connectingeach pair of coexistence groups that have coverage overlap, any pair ofoverlapping coexistence groups have different assigned colors andtherefore are not grouped together. Accordingly, grouping thecoexistence groups that have the same assigned color results innon-overlapping coexistence groups to be grouped together.

In one embodiment, the number of different colors assigned to thevertices in the vertex-colored graph of coexistence groups of accesspoints is the chromatic number which is the smallest number of colorsneeded to color the vertices of the graph so that no two adjacentvertices are assigned the same color. Obtaining vertex coloringscorresponding to the chromatic number may be performed according to anyalgorithms known to those skilled in the relevant arts. The resultingvertex-colored graph may then be used for shared spectrum resourceoptimization in any of the embodiments described herein. If there aremultiple options for vertex coloring corresponding to the chromaticnumber, each of the options may be considered as a candidate forobtaining shared spectrum resource assignment.

In some embodiments, since the shared spectrum is reused in eachconnected set, it may be advantageous from a spectrum efficiencyperspective to form as many connected sets as possible. Accordingly, aminimum cut or any other similar functionality may be used to formadditional connected sets in the vertex-colored graph. A minimum cut ofa graph is the cut with the lowest cost in terms of the weights thatwould be removed because of removing the corresponding connections/edgeswhen the graph is split by the cut. Once the minimum cut is performed, agraph coloring scheme such as a minimum coloring (i.e., coloring usingthe chromatic number of colors) may be used to provide candidate optionsfor obtaining shared spectrum resource assignment.

FIG. 3 illustrates a schematic diagram 3000 for dividing an original6-vertex connected set 3002, including vertices 3004 connected byweighted edges 3006, into a single-vertex connected set 3008 and a5-vertex connected set 3010 by applying a minimum cut 3012, and thenapplying minimum graph coloring to the single-vertex connected set 3008and to the 5-vertex connected set 3010 separately. In this example, thecost of the minimum cut 3012 is “1” since the single edge that isremoved by the minimum cut 3010 has a weight of “1”.

In some embodiments, when additional users request assignment of sharedspectrum resources, the cost of switching the resource assignments ofthe existing users may be significant, and therefore staying with thecurrent assignments may be desirable. Accordingly, these embodimentsinclude the current assignments as an option in the optimization ofshared spectrum resource assignments.

Some embodiments perform shared spectrum resource optimization byincluding, as additional options, “chromatic number plus 1” colors toobtain the colored-vertex graph, and/or splitting the colored-vertexgraph by cuts with overall removed weights that are the second smallestcompared to the minimum cut. These embodiments may result in smallergroups of coexistence groups (in terms of the number of access points ineach group of coexistence groups) and hence a reduced search space forshared spectrum resource assignment optimization.

Mapping of Groupings to Specific Frequencies

In any of the disclosed embodiments, after forming groups of coexistencegroups (e.g., such that there is no coverage area overlap between anytwo coexistence groups that are grouped together), the objectivefunction may be used to determine the best mapping of groupings tofrequencies. For example, if there are incumbents (primary users) suchas fixed satellite service (“FSS”) earth stations and/or Priority AccessLicense (“PAL”) Protection Areas (“PPAs”), the mapping of frequenciesmay be performed to maximize the objectives in terms of bandwidth andcoverage while ensuring protection of the incumbents. The objectivefunction may be used to compare various options and optimize the sharedspectrum resource assignments accordingly.

FIG. 4 illustrates a schematic diagram 4000 of an example embodiment forassigning specific frequencies to groupings of coexistence groups 1, 2,3, 4, and 5 with respective coverage areas 4004, 4006, 4008, 4010, and4012. In this example, an FSS earth station 4016 operates on frequencyf₁ near coexistence group 2, while a PAL (not shown) or incumbentprotection area 4014 (e.g., PPA) operates on frequency f₂ nearcoexistence groups 1 and 4. In one embodiment, the incumbent protectionarea 4014 and the protected FSS earth station 4016 are external to theshared spectrum region. The optimum shared spectrum assignment may beobtained by: first performing a minimum coloring to obtain thevertex-colored graph 4002 where coexistence groups 1, 3, and 4 areassigned the color blue and are therefore grouped together (the bluegroup) while coexistence groups 2 and 5 are assigned the color red andare therefore grouped together (the red group); and then assigning f₂ tothe red group (which does not include coexistence groups 1 and 4) and f₁to the blue group (which does not include coexistence group 2).

In an alternative embodiment, a suboptimum approach for shared spectrumassignment optimization includes grouping coexistence groups of accesspoints and mapping these groupings to a number of frequencies tomaximize an objective function while ignoring incumbent interferenceconstraints and/or allowing a remapping of individual access point powerlevels after the application of the optimization criteria. One suchsuboptimum approach includes equal partitioning of the interferencebudget over the access points and then performing reverse water fillingof the Effective Isotropic Radiated Power (“EIRP”) deficit of the accesspoints as described in detail below. In one embodiment, the EIRP of aradio transmitter is defined as the product of its transmit power andthe antenna gain in a given direction relative to that of an isotropicantenna.

In one embodiment, groups of coexistence groups of access points aremapped to frequencies without considering any incumbent protection, andthereafter, access point power levels are adjusted to ensure thatincumbents are protected from secondary user aggregate interferencewhile some fairness criteria are also satisfied. For example, in oneembodiment, if there are N access points capable, if operating at theirmaximum permissible power level, to cause harmful interference to anincumbent, a fair method to ensure incumbent protection is to firstallow each access point to contribute 1/N to the overall aggregateinterference at the incumbent. Under this measure of fairness, thecloser an access point is to the incumbent, the lower is the maximumtransmit power level of the access point. Since some access points maybe incapable of reaching the 1/N level of interference at the incumbent,it may be possible to allow some other access points to cause more thanthe 1/N level of interference at the incumbent. That is, some leftovermargin will exist that can be reassigned to other access points whilestill protecting the incumbent.

For an access point that is close to the incumbent, requiring the accesspoint to contribute 1/N to the overall aggregate interference at theincumbent may force the access point to operate at a power level that ismuch lower than its maximum permissible power level. In some cases, suchrequirement may lead to an unacceptably small access point coverage areafor access points that are too close to the incumbent. FIG. 5illustrates a schematic diagram 5000 where the power level PWR_(G) of agreen access point 5004 (a single access point belonging to a greengroup) and the power levels PWR_(B) of nine blue access points 5006(nine access points belonging to a blue group) are controlled to limitthe aggregate interference levels in an incumbent area of protection5002. In this example, the total number of access points N is 9+1=10,therefore each access point is allowed to contribute 1/N= 1/10 to theaggregate interference in the incumbent area of protection 5002. Thegreen access point 5004 is very close to location 5008 in the incumbentarea of protection 5002. In order for it to contribute 1/N to theaggregate interference at location 5008, the green access point 5004 inthis example is forced to operate at 37 dBm/10 MHz which is 10 dB belowits otherwise maximum permissible power level of 47 dBm. This results ina coverage area deficit for the green access point 5004. Meanwhile, theinterference contribution from the blue access points 5006 at location5008 is negligible due to their longer distance from location 5008.Thus, it is possible and preferable to allow the green access point 5004to use all the interference margin at this location.

However, further distributions of any remaining leftover margin using a1/N methodology will not resolve the severe transmit power and coveragearea deficit of the green access point 5004 as illustrated in FIGS. 6Aand 6B. Specifically, FIG. 6A provides a first bar graph 6000A of thegreen access point EIRP 6002 and blue access point EIRPs 6004 afterpower assignments that allow each of the ten access points to contribute1/N= 1/10 to the aggregate interference at location 5008, where thegreen access point 5004 is assigned 37 dBm while the each of the nineblue access points 5006 are assigned 46 dBm. Since the interferencecontribution of the blue access points 5006 at location 5008 isnegligible, each of the ten access points may be allowed to operate at ahigher power.

FIG. 6B provides a bar graph 6000B where water filling is performed suchthat the EIRP of each of the ten access points is equally increaseduntil the blue access points 5006 reach their maximum permissible powerlevel of 47 dBm. Generally, water filling refers to a method ofdistributing power that resembles the way water finds its level whenfilled in one part of a vessel with multiple openings/bins. In FIG. 6B,for SAS management of access points with limited water holding capacity(or in this case limited EIRP), water filling equally distributes theleftover margin to all access points under the constraint that a certainaccess point's total EIRP is capped at a certain level which may differacross access points. That is, water (or in this case the leftovermargin) fills up to that point, is capped, and then continues to fillthe other bins (or in this case the other access points). In otherwords, the leftover margin is distributed to access points up to theEIRP limit of each access point.

As illustrated in FIG. 6B, after water filling, the EIRP of the greenaccess point 5004 is increased by 1 dBm from 37 dBm to 38 dBm, whichdoes little to ameliorate the coverage gap for the green access point5004. In contrast, the nine blue access points 5006, which did not havesignificant coverage gap, also have their EIRPs increased by 1 dBm from46 dBm to 47 dBm, thus consuming most of the leftover margin withoutproviding significant coverage gain.

In one embodiment, the coverage area deficit of the green access point5004 may be ameliorated using “reverse water filling” as shown in FIGS.6C and 6D. Reverse water filling is different than water filling in thatnow water (or in this case the leftover margin) is first given to accesspoints with the largest EIRP deficit with the goal of equalizing theEIRP deficit across access points. After reverse water filling, thedeficit would be the same for all access points as shown in FIG. 6D. Insome embodiments, with reverse water filling, there may be more leftovermargin than the bins can take before overflowing (i.e., the EIRP deficitmay be reduced to zero for all access points and there is still someremaining leftover margin to distribute).

Specifically, after the initial 1/N allocation illustrated in FIG. 6A,the green access point 5004 has an EIRP deficit of 10 dBm while each ofthe blue access points 5006 have an EIRP deficit of 1 dBm. FIG. 6Cprovides a bar graph 6000C of a 10 dBm green access point EIRP deficit6006 and 1 dBm blue access point EIRP deficits 6008. Denoting by C_(i)the EIRP deficit (in dB) before reverse water filling for the i^(th)access point (47 dBm−37 dBm=10 dBm for the green access point 5004 and47 dBm−46 dBm=1 dBm for the blue access points 5006), the level γ ofreverse water filling 6010 is then chosen so that the EIRP deficit afterwater filling for each access point is min (γ, C_(i)) and the resultinginterference increase at location 5008 due to the reverse water fillingprocess equals the leftover aggregate interference margin at location5008. As such, any leftover margin is allocated first to access pointswith the most severe coverage deficit, in this case, the green accesspoint 5004. FIG. 6D provides a bar graph 6000D where the reverse waterfilling reduces the EIRP deficit to min (γ, C_(i)) where γ is chosen sothat the resulting interference increase equals the leftover aggregateinterference margin at location 5008.

FIG. 7 is a flowchart for assigning shared spectrum resources to variousaccess points, according to an embodiment of the disclosed subjectmatter. In various embodiments, the method may be executed by one ormore processor or microprocessors, microcontroller devices, or controllogic including integrated circuits such as application-specificintegrated circuits (ASICs). In some embodiments, the method may beexecuted in a cloud platform by one or more processors executing one ormore software modules.

At 7002 the access points are grouped into coexistence groups of accesspoints, and at 7004 a vertex graph including vertices that eachrepresent one of the coexistence groups is generated. In one embodiment,an edge connecting a pair of vertices in the vertex graph represents anoverlap between coverage contours of a pair of coexistence groupsrepresented by the pair of vertices. In one embodiment, the edge isassigned a weight that is proportional to the overlap as compared toother overlaps between coverage contours of other pairs of coexistencegroups.

At 7006 at least one vertex-colored graph is generated by assigning acolor to each vertex in the vertex graph, and at 7008 the coexistencegroups are grouped into groups of coexistence groups based on theircorresponding assigned colors in the at least one vertex-colored graph.At 7010 shared spectrum transmit frequencies are mapped to the groups ofcoexistence groups, where each access point in a group of coexistencegroups is configured to transmit using a transmit frequency that isassigned to the group of coexistence groups by the mapping.

In some embodiments the mapping of the shared spectrum transmitfrequencies to the groups of coexistence groups is performed based on anobjective function. In some embodiments, a transmit power level isassigned to each access point using the at least one vertex-coloredgraph along with the objective function. The objective function may haveobjective parameters including access point bandwidth and coverageareas, wherein the objective function increases as the objectiveparameters increase. The objective function may also have costparameters including interference costs and switching costs, where theobjective function decreases as the cost parameters increase, Theswitching cost may be indicative of a negative impact of a candidateassignment requiring an access point to change transmit frequency orpower. The interference costs may depend at least partly on weightsassigned to edges in the at least one vertex-colored graph. Theobjective function may also account for constraints including minimumaccess point bandwidth, minimum access point transmit power, incumbentprotection, or guard bands between access point frequency assignments.

In some embodiments, the method is performed by at least one SASimplemented as one or more software modules on a cloud platform. In someembodiments, the method is performed by coordination of at least twoSASs that share information to generate the at least one vertex-coloredgraph, where the SASs use the at least one vertex-colored graph alongwith a single common objective function to assign frequency and transmitpower levels to access points. The shared information may includeweights of edges in the at least one vertex-colored graph.

In some embodiments, all coexistence groups in a same group ofcoexistence groups have a same assigned color in the at least onevertex-colored graph. In some embodiments, no edge of the at least onevertex-colored graph is connecting two vertices that have a sameassigned color. In some embodiments, the vertices are colored bydetermining a chromatic number and determining vertex coloringscorresponding to the chromatic number.

In some embodiments, the vertex graph includes two or more connectedsets, where vertices in each connected set are colored independently ofother connected sets to generate two or more vertex-colored graphs. Inthese embodiments, the grouping of the coexistence groups is performedseparately on each of the two or more vertex-colored graphs. In someembodiments, the mapping of the shared spectrum transmit frequencies tothe groups of coexistence groups is performed based on an objectivefunction, and in each connected set, a transmit power level is assignedto each access point using a corresponding vertex-colored graph alongwith the objective function.

In some embodiments, the two or more connected sets are created byapplying at least one cut on the vertex graph. In some embodiments, theat least one cut is a minimum cut of the vertex graph along a set ofedges with a lowest aggregate edge weight. In some embodiments, the atleast one vertex-colored graph is used along with the objective functionto maximize bandwidth and coverage area of the access points whileminimizing interference to an incumbent device. In some embodiments, theat least one vertex-colored graph is used along with the objectivefunction to maximize bandwidth and coverage area of the access pointswhile minimizing interference to locations in a protected area.

In some embodiments, the at least one vertex-colored graph is used alongwith the objective function to maximize bandwidth and coverage area ofthe access points without minimizing interference to an incumbentdevice. In these embodiments, after maximizing bandwidth and coveragearea of the access points without minimizing interference to anincumbent device, access point transmit power levels are adjusted tominimize an aggregate interference to an incumbent device. The accesspoint transmit power levels may be adjusted by applying a fairnesscriterion where each access point is permitted to contribute 1/N to theaggregate interference to the incumbent device, where N is the number ofaccess points interfering with the incumbent device.

The access point transmit power levels may further be adjusted by, afterapplying the fairness criterion to compute an initial fair powerallocation and using the fair power allocations across all access pointsto compute the initial aggregate interference to the incumbent device,determining a leftover margin on the aggregate interference to theincumbent device, determining EIRP deficits for each access point basedon access point requested transmit power levels (i.e., the power levelsthat the access points request from a corresponding managing SAS) andpower determined by applying the fairness criterion, and applying alevel of reverse water filling of power over the access points suchthat: (A) the EIRP deficit after the reverse water filling is the samefor all access points, and (B) the resulting aggregate interferenceincrease at the incumbent device after the reverse water filling is lessthan or equal to the leftover margin.

As disclosed, embodiments provide SAS functionality to conduct resourceassignment across coexistence groups of access points. The SASfunctionality may include combining two or more coexistence groups touse the same channel, determining fair bandwidth allocation to thecoexistence group combination, mapping the bandwidth allocation tospecific frequencies, choosing fair power assignment for each accesspoint, and sharing information with other SASs to coordinate resourceassignments. These functionalities may be performed jointly orseparately.

Any functionality disclosed herein with reference to various embodimentsmay be implemented by a server/computer which may be a personal computeror workstation or other such computing system that includes a processor.However, alternative embodiments may implement more than one processorand/or one or more microprocessors, microcontroller devices, or controllogic including integrated circuits such as ASIC. A bus may providecommunication among various modules of the server/computer such as aprocessor and a memory so that the processor may executes instructionsstored on the memory. The instructions may be compiled from sourcecode/objects in a programming language such as Java, C++, C#, .net,Visual Basic™ language, LabVIEW, or another structured orobject-oriented programming language. The memory may removable ornon-removable, and may include any volatile or non-transitorycomputer-readable medium that can be read by the server/computer such asROM, PROM, EEPROM, RAM, flash memory, disk drive, etc.

The systems and methods described above may be implemented by anyhardware, software, or a combination of hardware and software having theabove-described functions. The software code, either in its entirety ora part thereof, may be stored in a computer-readable memory.

While several implementations have been provided in the presentdisclosure, it should be understood that the disclosed systems andmethods may be implemented in many other specific forms withoutdeparting from the scope of the present disclosure. The present examplesare to be considered as illustrative and not restrictive, and theintention is not to be limited to the details given herein. For example,the various elements or components may be combined or integrated inanother system or certain features may be omitted, or not implemented.

Also, techniques, systems, subsystems, and methods described andillustrated in the various implementations as discrete or separate maybe combined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component, whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

While the above detailed description has shown, described, and pointedout the fundamental novel features of the disclosure as applied tovarious implementations, it will be understood that various omissionsand substitutions and changes in the form and details of the systemillustrated may be made by those skilled in the art, without departingfrom the intent of the disclosure.

What is claimed is:
 1. A method for assigning shared spectrum resourcesto access points, comprising: grouping the access points intocoexistence groups of access points; generating a vertex graph includingvertices that each represent one of the coexistence groups, wherein aconnection in the vertex graph between a pair of the verticesrepresenting a pair of the coexistence groups is assigned a weight basedon an amount of interference between the pair of the coexistence groups;generating at least one vertex-colored graph by assigning a color toeach vertex in the vertex graph; grouping the coexistence groups intogroups of coexistence groups based on their corresponding assignedcolors in the at least one vertex-colored graph; and mapping sharedspectrum transmit frequencies to the groups of coexistence groups,wherein each access point in a group of coexistence groups is configuredto transmit using a transmit frequency that is assigned to the group ofcoexistence groups by the mapping.
 2. The method of claim 1, wherein themapping of the shared spectrum transmit frequencies to the groups ofcoexistence groups is performed based on an objective function, themethod further comprising: assigning a transmit power level to eachaccess point using the at least one vertex-colored graph along with theobjective function.
 3. The method of claim 2, wherein the objectivefunction has objective parameters including access point bandwidth andcoverage areas, wherein the objective function increases as theobjective parameters increase.
 4. The method of claim 2, wherein theobjective function has cost parameters including interference costs andswitching costs, wherein the objective function decreases as the costparameters increase, wherein the switching cost is indicative of anegative impact of a candidate assignment requiring an access point tochange transmit frequency or power, wherein the interference costsdepend at least partly on weights assigned to the connections in the atleast one vertex-colored graph.
 5. The method of claim 2, wherein theobjective function accounts for constraints including minimum accesspoint bandwidth, minimum access point transmit power, incumbentprotection, or guard bands between access point frequency assignments.6. The method of claim 1, wherein the method is performed by at leastone Spectrum Access System (SAS) implemented as one or more softwaremodules on a cloud platform.
 7. The method of claim 1, wherein themethod is performed by coordination of at least two Spectrum AccessSystems (SASs) that share information to generate the at least onevertex-colored graph, wherein the SASs use the at least onevertex-colored graph along with a single common objective function toassign frequency and transmit power levels to access points, wherein theshared information includes the weights of the connections in the atleast one vertex-colored graph.
 8. The method of claim 1, wherein allcoexistence groups in a same group of coexistence groups have a sameassigned color in the at least one vertex-colored graph, wherein noconnection of the at least one vertex-colored graph is connecting twovertices that have a same assigned color.
 9. The method of claim 1,wherein the vertices are colored by determining a chromatic number anddetermining vertex colorings corresponding to the chromatic number. 10.The method of claim 1, wherein the vertex graph comprises two or moreconnected sets, wherein vertices in each connected set are coloredindependently of other connected sets to generate two or morevertex-colored graphs, wherein the grouping of the coexistence groups isperformed separately on each of the two or more vertex-colored graphs.11. The method of claim 10, wherein the mapping of the shared spectrumtransmit frequencies to the groups of coexistence groups is performedbased on an objective function, the method further comprising: in eachconnected set, assigning a transmit power level to each access pointusing a corresponding vertex-colored graph along with the objectivefunction.
 12. The method of claim 10, wherein the two or more connectedsets are created by applying at least one cut on the vertex graph,wherein the at least one cut is a minimum cut of the vertex graph alonga set of the connections with a lowest aggregate connection weight. 13.The method of claim 2, wherein the at least one vertex-colored graph isused along with the objective function to maximize bandwidth andcoverage area of the access points while minimizing interference tolocations in a protected area.
 14. The method of claim 2, wherein the atleast one vertex-colored graph is used along with the objective functionto maximize bandwidth and coverage area of the access points whileminimizing interference to an incumbent device.
 15. The method of claim2, wherein the at least one vertex-colored graph is used along with theobjective function to maximize bandwidth and coverage area of the accesspoints without minimizing interference to an incumbent device.
 16. Themethod of claim 15, wherein, after maximizing bandwidth and coveragearea of the access points without minimizing interference to anincumbent device, access point transmit power levels are adjusted tominimize an aggregate interference to an incumbent device.
 17. Themethod of claim 16, wherein the access point transmit power levels areadjusted by applying a fairness criterion where each access point ispermitted to contribute 1/N to the aggregate interference to theincumbent device, wherein N is the number of access points interferingwith the incumbent device.
 18. The method of claim 17, wherein theaccess point transmit power levels are further adjusted by: afterapplying the fairness criterion, determining a leftover margin on theaggregate interference to the incumbent device; determining EffectiveIsotropic Radiated Power (EIRP) deficits for each access point based onaccess point requested transmit power levels and the power determined byapplying the fairness criterion; and applying a level of reverse waterfilling of power over the access points such that: (A) the EIRP deficitafter the reverse water filling is the same for all access points, and(B) the resulting aggregate interference increase at the incumbentdevice after the reverse water filling is less than or equal to theleftover margin.
 19. A non-transitory computer-readable medium storinginstructions that, when executed by a processor, cause the processor toassign shared spectrum resources to access points, the assigningcomprising: grouping the access points into coexistence groups of accesspoints; calculating an amount of interference between the coexistencegroups; generating a vertex graph including vertices that each representone of the coexistence groups, wherein a connection in the vertex graphbetween a pair of the vertices representing a pair of the coexistencegroups is assigned a weight based on an amount of interference betweenthe pair of the coexistence groups; generating at least onevertex-colored graph by assigning a color to each vertex in the vertexgraph; grouping the coexistence groups into groups of coexistence groupsbased on their corresponding assigned colors in the at least onevertex-colored graph; and mapping shared spectrum transmit frequenciesto the groups of coexistence groups, wherein each access point in agroup of coexistence groups is configured to transmit using a transmitfrequency that is assigned to the group of coexistence groups by themapping.
 20. A network system, comprising: one or more servers; and twoor more Spectrum Access Systems (SASs) implemented as software moduleshosted on the one or more servers, wherein the two or more SASs areconfigured to communicate with each other and with access points toassign shared spectrum resources to the access points, the assigningcomprising: grouping the access points into coexistence groups of accesspoints; calculating an amount of interference between the coexistencegroups; generating a vertex graph including vertices that each representone of the coexistence groups, wherein a connection in the vertex graphbetween a pair of the vertices representing a pair of the coexistencegroups is assigned a weight based on an amount of interference betweenthe pair of the coexistence groups; generating at least onevertex-colored graph by assigning a color to each vertex in the vertexgraph; grouping the coexistence groups into groups of coexistence groupsbased on their corresponding assigned colors in the at least onevertex-colored graph; and mapping shared spectrum transmit frequenciesto the groups of coexistence groups, wherein each access point in agroup of coexistence groups is configured to transmit using a transmitfrequency that is assigned to the group of coexistence groups by themapping.
 21. The network system of claim 20, wherein the weight assignedto the connection between the pair of the coexistence groups is furtherbased on a comparison of the interference between the pair of thecoexistence groups as against an amount of interference between anotherpair of the coexistence groups.
 22. The non-transitory computer-readablemedium of claim 19, wherein the weight assigned to the connectionbetween the pair of the coexistence groups is further based on acomparison of the interference between the pair of the coexistencegroups as against an amount of interference between another pair of thecoexistence groups.
 23. The method of claim 1, wherein the weightassigned to the connection between the pair of the coexistence groups isfurther based on a comparison of the interference between the pair ofthe coexistence groups as against an amount of interference betweenanother pair of the coexistence groups.